elf: Allow arch to tweak initial mmap prot flags

An arch may want to tweak the mmap prot flags for an
ELFexecutable's initial mappings.  For example, arm64 is going to
need to add PROT_BTI for executable pages in an ELF process whose
executable is marked as using Branch Target Identification (an
ARMv8.5-A control flow integrity feature).

So that this can be done in a generic way, add a hook
arch_elf_adjust_prot() to modify the prot flags as desired: arches
can select CONFIG_HAVE_ELF_PROT and implement their own backend
where necessary.

By default, leave the prot flags unchanged.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 1fb67e506b68..cceb29d6ef1d 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -544,7 +544,8 @@ static inline int arch_check_elf(struct elfhdr *ehdr, bool has_interp,
 
 #endif /* !CONFIG_ARCH_BINFMT_ELF_STATE */
 
-static inline int make_prot(u32 p_flags)
+static inline int make_prot(u32 p_flags, struct arch_elf_state *arch_state,
+			    bool has_interp, bool is_interp)
 {
 	int prot = 0;
 
@@ -554,7 +555,8 @@ static inline int make_prot(u32 p_flags)
 		prot |= PROT_WRITE;
 	if (p_flags & PF_X)
 		prot |= PROT_EXEC;
-	return prot;
+
+	return arch_elf_adjust_prot(prot, arch_state, has_interp, is_interp);
 }
 
 /* This is much more generalized than the library routine read function,
@@ -564,7 +566,8 @@ static inline int make_prot(u32 p_flags)
 
 static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 		struct file *interpreter,
-		unsigned long no_base, struct elf_phdr *interp_elf_phdata)
+		unsigned long no_base, struct elf_phdr *interp_elf_phdata,
+		struct arch_elf_state *arch_state)
 {
 	struct elf_phdr *eppnt;
 	unsigned long load_addr = 0;
@@ -596,7 +599,8 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 	for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
 		if (eppnt->p_type == PT_LOAD) {
 			int elf_type = MAP_PRIVATE | MAP_DENYWRITE;
-			int elf_prot = make_prot(eppnt->p_flags);
+			int elf_prot = make_prot(eppnt->p_flags, arch_state,
+						 true, true);
 			unsigned long vaddr = 0;
 			unsigned long k, map_addr;
 
@@ -1041,7 +1045,8 @@ out_free_interp:
 			}
 		}
 
-		elf_prot = make_prot(elf_ppnt->p_flags);
+		elf_prot = make_prot(elf_ppnt->p_flags, &arch_state,
+				     !!interpreter, false);
 
 		elf_flags = MAP_PRIVATE | MAP_DENYWRITE | MAP_EXECUTABLE;
 
@@ -1184,7 +1189,8 @@ out_free_interp:
 	if (interpreter) {
 		elf_entry = load_elf_interp(&loc->interp_elf_ex,
 					    interpreter,
-					    load_bias, interp_elf_phdata);
+					    load_bias, interp_elf_phdata,
+					    &arch_state);
 		if (!IS_ERR((void *)elf_entry)) {
 			/*
 			 * load_elf_interp() returns relocation